Commercial processes for the preparation of alkylene glycols, for example, ethylene glycol, propylene glycol and butylene glycol, involve the liquid-phase hydration of the corresponding alkylene oxide in the presence of a large molar excess of water (see, for example, Kirk-Othmer, Encyclopedia of Chemical Technology, Vol. 11, Third Edition, page 929 (1980)). The hydrolysis reaction is typically conducted at moderate temperatures, e.g., about 100 to about 200.degree. C., with water being provided to the reaction zone in excess of 15 moles per mole of alkylene oxide. The primary by-products of the hydrolysis reaction are di- and polyglycols, e.g., dialkylene glycol, trialkylene glycol and tetra-alkylene glycol. The formation of the di- and polyglycols is believed to be primarily due to the reaction of alkylene oxide with alkylene glycol. As alkylene oxides are generally more reactive with alkylene glycols than they are with water, the large excesses of water are employed in order to favor the reaction with water and thereby obtain a commercially attractive selectivity to the monoglycol product.
Since the alkylene glycols must be recovered from the hydrolysis reaction mixtures, the large excess of water can result in an energy intensive procedure. Typically, the water is removed by evaporation to leave an alkylene glycol containing residue which is -purified by distillation. Hence, a reduction in the amount of water employed while maintaining, or enhancing, selectivity toward the monoglycol product could be beneficial from the standpoint of energy efficiency.
The hydrolysis reaction proceeds uncatalyzed; however, the presence of acids or bases enhance the rate of reaction. Acid and base catalysts, however, do have shortcomings. For instance, base catalysts are generally not selective to the formation of the monoglycol product and acid catalysts are typically associated with corrosion problems. Hence, commercial processes typically utilize relatively neutral hydrolysis conditions (for instance, pH 6-10).
Representative of the numerous acid catalysts that have been suggested for use in the hydration of alkylene oxides include fluorinated alkyl sulfonic acid ion exchange resins (U.S. Pat. No. 4,165,440); carboxylic acids and halogen acids (U.S. Pat. No. 4,112,054); strong acid cation exchange resins (U.S. Pat. No. 4,107,221); aliphatic mono- and/or polycarboxylic acids (U.S. Pat. No. 3,933,923); cationic exchange resins (U.S. Pat. No. 3,062,889); acidic zeolites (U.S. Pat. No. 3,028,434); sulfur dioxide (U.S. Pat. No. 2,807,651); trihalogen acetic acids (U.S. Pat. No. 2,472,417); and copper-promoted aluminum phosphate (U.S. Pat. No. 4,014,945).
In addition to the acid catalysts, numerous catalysts have been suggested for the hydration of alkylene oxides in the presence of carbon dioxide. These include alkali metal halides, such as chlorides, bromides and iodides; quaternary ammonium halides such as tetramethyl ammonium iodide and tetramethyl ammonium bromide (British Patent No. 1,177,877); organic tertiary amines such as triethylamine and pyridine (German published patent application 2,615,595, and U.S. Pat. No. 4,307,256); quaternary phosphonium salts (U.S. Pat. No 4,160,116); and partially amine-neutralized sulfonic acid catalyst, e.g., partially amine neutralized sulfonic acid resin (U.S. Pat. No. 4,393,254).
Various metal containing compounds, including metal oxides, have been proposed as catalysts for the hydrolysis of alkylene oxides. For example, U.S. Pat. No. 2,141,443 discloses the production of glycols by the reaction of alkylene oxide with water in the presence of a dehydrating metal oxide, for example, alumina, thoria, or oxides of tungsten, titanium, vanadium, molybdenum or zirconium. The reaction is carried out in the liquid phase and under conditions of temperature and pressure suited to maintain such phase. In example 7, the patentees disclose rendering a yellow tungstic acid catalyst more mechanically stable by admixture with a mixture of silicon ester, alcohol and water followed by drying the catalyst. Similarly, U.S. Pat. No. 2,807,651 states that it is known to catalyze the reaction of an alkylene oxide and water by alkali metal bases, alcoholates, oxides of titanium, tungsten and thorium, certain metal salts such as NiSO.sub.4, acid forming salts such as BF.sub.3, and the chlorides of Zn, Sn, and Fe, certain hydrosilicates and acidified hydrosilicates such as aluminum hydrosilicate, lower alkyl tertiary amines (such as trimethyl, triethyl and triamyl), and certain organic salts such as diethylsulfate.
Compounds of many of the transition metals and other metals such as vanadium, molybdenum, tungsten, titanium, chromium, zirconium, selenium, tellurium, tantalum, rhenium, uranium and niobium, have also been proposed as components for catalysts for preparing 1,2-epoxides of alpha-olefins and organic hydroperoxides and often are present during a subsequent hydrolysis reaction. For instance, Examples I and III of U.S. Pat. No. 3,475,499 disclose that a mixture of normal alpha-olefins containing 11 to 15 carbon atoms was epoxidized with ethylbenzene hydroperoxide in the presence of molybdenum naphthanate catalyst. After distillation, the bottoms which contained the 1,2-epoxides and the molybdenum-containing catalyst were contacted with water containing 0.5 percent sodium hydroxide at a temperature of 90.degree. C. That reaction product was distilled and a conversion of 1,2-epoxides was reported to be 100 percent and the selectivity to 1,2-glycols was reported to be 94 percent.
More recently, U.S. Pat. No. 4,277,632 discloses a process for the production of alkylene glycols by the hydrolysis of alkylene oxides in the presence of a catalyst of at least one member selected from the group consisting of molybdenum and tungsten. The patent discloses that the catalyst may be metallic molybdenum or metallic tungsten, or inorganic or organic compounds thereof, such as oxides, acids, halides, phosphorous compounds, polyacids, alkali metal and alkaline earth metal, ammonium salts and heavy metal salts of acids and polyacids, and organic acid salts. An objective of the disclosed process is stated to be the hydrolysis of alkylene oxides wherein water is present in about one to five times the stoichiometric value without forming appreciable amounts of by products such as the polyglycols. The reaction may be carried out in the presence of carbon dioxide; however, when the reaction is carried out in the presence of nitrogen, air, etc., the patentees state that the pH of the reaction mixture should be adjusted to a value in the range of 5 to 10. Japanese Kokai No. JA 54/128,507 discloses a process for the production of alkylene glycols from alkylene oxides and water using metallic tungsten and/or tungsten compounds.
Japanese Kokai No. JA 56/073,035 discloses a process for the hydrolysis of alkylene oxide under a carbon dioxide atmosphere in the presence of a catalyst consisting of a compound containing at least one element selected from the group of titanium, zirconium, vanadium, niobium, tantalum and chromium. The compounds include the oxides, sulfides, acids, halides, phosphorous compounds, polyacids, alkali metal salts of acids and polyacids, ammonium salts of acids and polyacids, and heavy metal salts of acids.
Japanese Kokai No. JA 56/073,036 discloses a process for the hydrolysis of alkylene oxide under a carbon dioxide atmosphere in the presence of a catalyst consisting of a compound containing at least one element selected from a group comprising aluminum, silicon, germanium, tin, lead, iron, cobalt and nickel.
Japanese Kokai No. JA 56/92228 is directed to processes for producing highly pure alkylene glycols. The disclosure is directed to a distillation procedure for recovery of a molybdenum and/or tungsten containing catalyst from an alkylene oxide hydrolysis process in the presence of carbon dioxide. The application states that the catalyst is at least one compound selected from the group consisting of compounds of molybdenum and tungsten which compound may be in combination with at least one additive selected from the group consisting of compounds of alkali metals, compounds of alkaline earth metals, quaternary ammonium salts and quaternary phosphonium salts. The preferred catalysts are stated to be molybdic acid, sodium molybdate, potassium molybdate, tungstic acid, sodium tungstate and potassium tungstate. Potassium iodide is the only additive employed in the examples.
U.S. Pat. No. 4,551,566 discloses the production of monoalkylene glycols with high selectivity by the reaction of a vicinal alkylene oxide with water in the presence of a water soluble metavanadate. Hence, lower water to alkylene oxide ratios can be employed using the disclosed process with attractive selectivities to the monoglycol products. The counter ion to the metavanadate is selected to provide a water soluble metavanadate salt under the reaction conditions employed and alkali metals, alkaline earth metals, quaternary ammonium, ammonium, copper, zinc, and iron are suggested cations. It is also disclosed that the metavanadate may be introduced into the reaction system in the salt form or on a support such as silica, alumina, zeolites and clay. Since the metavanadate ion is water-soluble, it can be lost from the reaction system and means must be provided to recover it from the effluent from the reaction zone.
Unfortunately, insoluble salts of vanadate anion, such as calcium vanadate, as well as insoluble molybdate and other metalate salts do not appear to provide the selectivity toward the monoglycol products which is achievable with the water-soluble metalates. The problems with the recovery of the metalate are significant factors in considering the use of the technology on a commercial scale.
Japanese Kokai No. JA 57/139,026 discloses a process for the hydrolysis of alkylene oxides in the presence of carbon dioxide and a halogen-type anion exchange resin as a catalyst. The exemplified catalyst is a chlorine-type anion exchange resin (Dowex MSA-1(TM), a product of the Dow Chemical Company) and a similar iodine-type anion exchange resin. At a mole ratio of alkylene oxide to water of about 0.66, the selectivity to monoethylene glycol was reported to be 91.0 percent using the chlorine-type anion exchange resin and 89.6 percent using the iodine-type anion exchange resin. In the absence of carbon dioxide, the application disclosed that a selectivity to the monoethylene glycol of 34.8 percent was obtained and an unpleasant smell was noted in the product. In the absence of any anion exchange resin and in the presence of carbon dioxide, the selectivity to monoethylene glycol was reported to be 37.5 percent. All of the examples were conducted in an autoclave immersed in an oil bath at a temperature of 150.degree. C. The disclosure reports that the maximum reaction liquid temperature was 130.degree. C. and the reaction was carried out for 90 minutes. While the application did not specifically indicate the source of the unpleasant smell which originated in the comparative example where the carbon dioxide atmosphere was not employed, it could have been the result of degradation of the anion exchange resin.
U.S. Pat. No. 4,579,982 is directed to processes for the hydrolysis of alkylene oxide with enhanced selectivities to monoalkylene glycols using a reaction menstruum comprising an aqueous phase, a water-immiscible liquid phase and a metalate anion-containing material wherein the concentration of the metalate anion containing material in the water immiscible phase is greater than that in the aqueous phase.
Copending U.S. patent application Ser. No. 594,268, herein incorporated by reference, discloses a process for the hydrolysis of alkylene oxide to form the corresponding alkylene glycol in the presence of a selectivity enhancing metalate anion which is in association with electropositive complexing sites on a solid support. The selectivity-enhancing metalate anion is characterized as an anion containing a polyvalent metal having a double bonded oxygen thereon. The anion, in free-ionic form or in association with a solid support, enhances the selectivity of the hydrolysis reaction to the monoalkylene glycol. This application further discloses the hydrolysis can be conducted as a batch reaction or as a continuous process and that during the continuous process the hydrolysis can occur in one or several zones, all or some of which contain the metalate-containing solid support.
It is the purpose of the present invention to provide an improved process for the hydrolysis of alkylene oxide in the presence of a selectivity-enhancing metalate-containing solid catalyst which process provides a significantly more efficient use of the catalyst, without a significant loss in selectivity.